Ruby-on-rails Rails：找到与 where 子句的深层嵌套关联

Rails: Finding a deeply nested association with a where clause

提问by nullnullnull

I have two models joined with a has_many :through relationship:

我有两个模型加入了 has_many :through 关系：

class Publication < ActiveRecord::Base
  has_many :publication_contributors
  has_many :contributors, :through => :publication_contributors
end

class Contributor < ActiveRecord::Base
  has_many :publication_contributors
  has_many :publications, :through => :publication_contributors
end

class PublicationContributor < ActiveRecord::Base
  belongs_to :publication
  belongs_to :contributor
end

(Something unusual and important about my PublicationContributor model is that it has more than just a pair of database ids, it also has a string attribute called contributor_type. This string could contain roles such as "Author" or "Translator" or "Publisher". I don't believe this is the problem here, but a solution must still account for it.)

（我的 PublicationContributor 模型不寻常且重要的一点是，它不仅具有一对数据库 ID，还具有一个名为contributor_type 的字符串属性。该字符串可以包含诸如“作者”或“翻译者”或“出版者”之类的角色。我不相信这是这里的问题，但解决方案仍然必须解决它。）

I want to find a Publication that has specific contributors like so:

我想找到一个具有特定贡献者的出版物，如下所示：

Publication
  .joins(:publication_contributors =>  :contributor)
  .where(:publication_contributors => 
            {:contributor_type => "Author", 
             :contributor => {:name => params[:authors]}})

Everything works fine until I get to the nested :contributor, at which point the SQL sputters:

一切正常，直到我到达嵌套的 :contributor，此时 SQL 出现异常：

Mysql2::Error: Unknown column 'publication_contributors.contributor' in 'where clause'

Rather than looking for publication_contributors.contributor_id, it's looking for publication_contributors.contributor, which doesn't exist. Am I doing something wrong in my code? I can't find any other examples of a where clause with deeply nested associations like this. Perhaps it's not even possible?

它不是在寻找publication_contributors.contributor_id，而是在寻找并不存在的publication_contributors.contributor。我的代码做错了吗？我找不到像这样具有深层嵌套关联的 where 子句的任何其他示例。也许它甚至不可能？

UPDATE:

更新：

The generated SQL

生成的 SQL

←[1m←[35mPublication Load (0.0ms)←[0m  SELECT `publications`.* FROM `publicati
ons` INNER JOIN `publication_contributors` ON `publication_contributors`.`public
ation_id` = `publications`.`id` INNER JOIN `contributors` ON `contributors`.`id`
 = `publication_contributors`.`contributor_id` WHERE `publication_contributors`.
`contributor_type` = 'Author' AND `publication_contributors`.`contributor` = '--
-\n:name:\n- Marilynne Robinson\n' LIMIT 1

Also, I have this association in my Publications model:

另外，我的 Publications 模型中有这个关联：

has_many :authors, :through => :publication_contributors, :source => :contributor, :conditions => {:publication_contributors => {:contributor_type => "Author"}}

I was thinking that I could do this:

我在想我可以这样做：

Publication.joins(:authors).where(:authors => {:name => params[:authors]})

But that throws the error:

但这会引发错误：

Mysql2::Error: Unknown column 'authors.name' in 'where clause'

回答by m_x

try to change your where clause :

尝试更改您的 where 子句：

Publication
  .joins( :publication_contributors => :contributor )
  .where( :publication_contributors => {:contributor_type => "Author"}, 
          :contributors             => {:name => params[:authors]} ) 

ActiveRecord api is not extremely consistent here : the arguments for wheredo not work exactly as those for joins. This is because the arguments for joinsdo notreflect the underlying SQL, whereas the arguments for wheredo.

ActiveRecord api 在这里不是非常一致： 的参数where与joins. 这是因为，参数joins做不反映基础SQL，而论据where做的。

whereaccepts an hash whose keys are table names, and values are hashes (that themselves have column names as keys). It just prevents ambiguity when targetting a column that has the same name in two tables.

where接受一个哈希，其键是表名，值是哈希（它们本身以列名作为键）。它只是在定位两个表中具有相同名称的列时防止歧义。

This also explains why your second problem arises : the relation authorsdoes not exist.

这也解释了为什么会出现第二个问题：关系authors不存在。